1. Field of the Invention
The present invention relates generally to forming or joining of materials, and more particularly to an apparatus for the electromagnetic forming, joining or welding (EMF) of materials.
2. Description of the Related Art
Electromagnetic forming has long been used as a method of manipulating tubular components. Electromagnetic forming forces one workpiece against another resulting in the welding or joining of the workpieces. A weld occurs when molecular interaction takes place between the two workpieces and they are merged together at the molecular level. Joining occurs where there is no molecular interaction between the two workpieces.
U.S. Pat. Nos. 5,966,813; 6,104,012 and 5,981,921 disclose methods of joining tubular end fittings to drive shafts utilizing EMF. These patents incorporate a coil having individual segments connected in parallel similar to a coil design disclosed in U.S. Pat. No. 4,129,846. The inductance generated with this individual segment coil design requires very high amounts of imputed energy to generate adequately secured joints. The efficiencies of this coil design are insufficient for large-scale production and there is a need in the art for a more effective coil design.
Other designs have attempted to overcome the aforementioned shortcomings by using other coil designs. U.S. Pat. Nos. 3,654,787 and 5,442,846 disclose multi-turn coils adapted to surround tubular components by dividing the cylindrically wound coil to create two symmetrical C-shaped members. The coil can then be opened and clamped around tubular components thereby encircling the workpiece. A limitation of this design is the contact interface between the two coil halves when the electric current is moved through the coil. The high intensity of this current rapidly degrades this interface leading to an inconsistent EMF pressure pulse on the tubular component.
An attempt to resolve interface degradation between the coils is shown in U.S. Pat. No.6,229,125. In this embodiment two separate single turn coils connected inductively are clamped around the tubular component. Because the current is independently routed through the tubular components there is no interface that the current must negotiate and no concentrated interface degradation. However, because single turn coils are utilized, the electrical efficiency of the overall system is compromised. There exists a need for an multi-coiled electromagnetic forming apparatus that can be opened and closed around tubular components permitting EMF in areas accessible by a clamshell type design.
With EMF, high temperatures can be generated, thus necessitating a need for cooling. U.S. Pat. No. 3,842,630 suggests a method of cooling an electromagnetic forming apparatus by routing coolant through channels machined inside the coil. This approach does not actively cool the tool as the working area of the coil is not in direct contact with the coolant. U.S. Pat. No. 3,195,335 discloses pumping coolant to the turns of an electromagnetic forming coil. This design cannot be effectively utilized to trace all curves of an electromagnetic forming coil without breaking the coolant delivery tubes. There further exists a need to actively cool the EMF permitting higher rates of production without overheating.